OK, I believe I have it down. On the Chesapeake from the head to just North of Baltimore is considered "fresh". Then there are 3 stages of brackish below that point. It is Oligohine where the salinity is .5 to 10 ppt (parts per thousand) is from north of Baltimore to the Bay Bridge. It is Mesohaline (salinity 10.7-18.0ppt) from the Bay Bridge to the Rappanannock (medium salinity). It is Polyhaline (18.7-36ppt) from the Rappohannock to the ocean (36ppt is ocean water). So if Aluminum alloy anodes are made for brackish water the Chesapeake is definitely the place to use them. Also, I read a zinc anode can form a layer of zinc oxide insulating itself, then the protected metal will deteriorate. So upon reading this I've ordered all aluminum alloy anodes (Non Chinese) and will put on our boat. I've used zinc my whole boating history on the bay, I wonder how much easier some of those outdrive and lower unit tear downs would have went if they were protected with Aluminum alloy anodes. BTW its aluminum ALLOY so this anode is less noble than straight aluminum.

This is a change of thinking and might seem strange but I remember seeing that first computer at work and thinking "Yeah, that'll be out of here soon".

Why fix what ain't broke?

If you don't have any evidence of galvanic corrosion, using cheap and commonly available zinc anodes, why change?